Communication system designers are constantly seeking ways to improve the performance of system components and signal processing circuits, without incurring a substantial cost or hardware complexity penalty. For example, radio wave system designers desire to maximize the collection or emission of desired electromagnetic energy and to minimize the coupling of unwanted radiation with respect to the system's antenna. In communication systems that employ dipole antennas and arrays, such as those mounted on aircraft, for example, improvements in directivity gain can be obtained by Yagi antenna configurations that employ parasitic elements in proximity to driven dipole radiators. For an illustration of documentation that describes use of parasitic elements in antenna architectures, especially for improving directivity gain, including those employing dipole antennas, attention may be directed to the U.S. Pat. Nos. to Finneburgh, No. 2,897,497; Cermignami et al, Nos. 4,186,400 and 4,514,734; Coe et al, No. 4,812,855; and Podell, No. 5,612,706.
In high user density environments such as cellular wireless systems, mutual interference is perhaps the most significant problem. Although cell and channel assignment algorithms provide some measure of interference rejection, the fact remains that optimal performance requires that systems of this type have the ability to maximize energy coupling (such as between a subscriber unit and a base station) in a relatively narrow main lobe (namely, place the antennas main lobe `right on top` of a target emitter/receiver). In addition, they should reduce/minimize, to the extent possible, energy that is present in lobes other than the main beam, namely from sources (of interference) other than that lying in the main beam.